System and method for optical alignment and calibration of an infrared camera lens

ABSTRACT

A system for optical alignment and calibration of an infrared camera lens, including: a lens support mechanism configured to adjust a position of an infrared camera lens relative to a camera body that includes: a hexapod platform and a robotic arm to manipulate the position of the infrared camera lens that extends from the hexapod platform and is coupled thereto to be continually oriented parallel to the hexapod platform and to maintain the infrared camera lens continually oriented parallel to the orientation of the hexapod platform; at least one collimator configured to output infrared rays, wherein the at least one collimator is positioned such that the output infrared rays converge on an infrared sensor within the camera body through the infrared camera lens; and at least one curing catalyst configured to cure an adhesive placed on the infrared camera lens when an ideal lens position is determined.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/699,894 filed on Dec. 2, 2019, now allowed, the contents of which arehereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to camera lens calibration, andmore specifically to the initial alignment and calibration of infraredcamera lenses.

BACKGROUND

As sensor-based technology has improved dramatically in recent years,new uses for sensors have become possible. In particular, cameras havebecome widely utilized for various applications, including advanceddriver assistance systems (ADAS) and autonomous vehicle systems. Onetype of camera that may be utilized in these applications is a thermalinfrared camera. The infrared spectrum lies outside of the visible lightrange and consists of a near infrared section (NIR) with wavelengths of0.75-1 micrometers (μm); a short wavelength infrared section (SWIR) withwavelengths of 1-3 μm; a medium wavelength infrared section (MWIR) withwavelengths of 3-5 μm; and a long wavelength infrared section (LWIR)with wavelengths of 8-14 μm. Many thermal infrared (IR) cameras operatewithin the LWIR section to detect infrared energy that is guided to anIR sensor through the camera's lens. These IR cameras can be utilizedfor a variety of imaging applications including, but not limited to,passive motion detection, night vision, thermal mapping, health care,building inspection, surveillance, ADAS, and the like.

During the manufacture of an infrared camera, a lens should be attachedto the camera body, namely the element of the camera housing an infraredimage sensor. This attachment should be performed to exacting standards,as the lens must not only be placed at an ideal distance from thesensor, but in an ideal plane, since any minor shift or skewedpositioning will result in subpar or out of focus images. Therefore, thelens should be secured to the camera body with optimal positioning alongthe six degrees of freedom. Attaching a lens in such a precise mannermanually is not only ineffective, but difficult to replicate on aconsistent basis, let alone accomplish in an efficient manner. Further,even though robotic arms may be used to execute the attachment andreliably repeat the same movements from camera to camera, each lens andsensor may vary ever so slightly, requiring a unique and individualizedattachment for each pairing of a sensor and a lens, proving a difficulttask for a generic robot.

It would therefore be advantageous to provide a solution that wouldovercome the challenges noted above.

SUMMARY

A summary of several example embodiments of the disclosure follows. Thissummary is provided for the convenience of the reader to provide a basicunderstanding of such embodiments and does not wholly define the breadthof the disclosure. This summary is not an extensive overview of allcontemplated embodiments, and is intended to neither identify key orcritical elements of all embodiments nor to delineate the scope of anyor all aspects. Its sole purpose is to present some concepts of one ormore embodiments in a simplified form as a prelude to the more detaileddescription that is presented later. For convenience, the term “certainembodiments” may be used herein to refer to a single embodiment ormultiple embodiments of the disclosure.

Certain embodiments disclosed herein include a system for opticalalignment and calibration of an infrared camera lens, including: a lenssupport mechanism configured to adjust a position of an infrared cameralens relative to a camera body wherein the lens support mechanismfurther includes: a hexapod platform configured to move in six degreesof freedom; and a robotic arm configured to manipulate the position ofthe infrared camera lens, the robotic arm extending from the hexapodplatform and being coupled thereto so as to be continually orientedparallel to an orientation of the hexapod platform and to maintain theinfrared camera lens continually oriented parallel to the orientation ofthe hexapod platform; at least one collimator configured to outputinfrared rays, wherein the at least one collimator is positioned suchthat the output infrared rays converge on an infrared sensor within thecamera body through the infrared camera lens; and a curing catalystconfigured to cure an adhesive placed on the infrared camera lens whenan ideal lens position is determined.

Certain embodiments disclosed herein also include a method for opticalalignment and calibration of an infrared camera lens, including:applying an adhesive to an infrared camera lens, wherein the adhesive isconfigured to be cured by a curing catalyst; placing the infrared cameralens on a camera body using an adjustable arm extending from a hexapodplatform and being coupled thereto so as to be continually orientedparallel to an orientation of the hexapod platform and to maintain theinfrared camera lens continually oriented parallel to the orientation ofthe hexapod platform; determining an ideal lens position based on atleast a calibration target and a modulation transfer function (MTF)chart associated thereto; adjusting the position of the infrared cameralens based on the determined ideal lens position using the adjustablearm; and curing the adhesive with the curing catalyst and fixing theinfrared camera lens in place.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter disclosed herein is particularly pointed out anddistinctly claimed in the claims at the conclusion of the specification.The foregoing and other objects, features, and advantages of thedisclosed embodiments will be apparent from the following detaileddescription taken in conjunction with the accompanying drawings.

FIG. 1 is a schematic diagram of a system for optical alignment andcalibration of an infrared camera lens according to an embodiment.

FIG. 2A is a schematic diagram of a calibration target according to anembodiment.

FIG. 2B is an example screenshot of a multiple calibration targets assee through a calibration system.

FIG. 3 is an example screenshot of multiple modulation transfer function(MTF) charts projected onto an image of the calibration targets aftercalibration has been completed.

FIG. 4 is an example flowchart illustrating a method for attaching andaligning an infrared camera lens according an embodiment.

FIG. 5 is an example setup of an infrared lens alignment system andcuring lights, according to an embodiment.

DETAILED DESCRIPTION

It is important to note that the embodiments disclosed herein are onlyexamples of the many advantageous uses of the innovative teachingsherein. In general, statements made in the specification of the presentapplication do not necessarily limit any of the various claimedembodiments. Moreover, some statements may apply to some inventivefeatures but not to others. In general, unless otherwise indicated,singular elements may be in plural and vice versa with no loss ofgenerality. In the drawings, like numerals refer to like parts throughseveral views.

FIG. 1 is a schematic diagram of a system 100 for optical alignment andcalibration of an infrared camera lens 120 according to an embodiment.The system 100 includes one or more collimators 150 placed directlyabove a lens 120, such as an infrared lens, to be used for lenscalibration. A lens support mechanism of the system 100 includes arobotic arm 140 configured to hold the lens 120 and manipulate itsposition relative to a camera body 110. In an embodiment, the roboticarm 140 is supported by a hexapod platform 145. In an exampleembodiment, the platform 145 is configured to move the robotic arm 140,and the lens attached thereto 120, in a predefined number (e.g., 6)degrees of freedom. In a further embodiment, the hexapod platform 145 isa Steward platform with a high-resolution kinematic system employingthree pairs of hydraulic, pneumatic, or electro-mechanical actuatorsconfigured to adjust the x, y, and z axes along with the pitch, roll,and yaw. This allows for precise adjustments to the positioning of therobotic arm 140 attached thereto and thus to the lens 120. In anembodiment, the hexapod is controlled by software, or hardwareconfigured to run such software, that is configured to adjust thehexapod according to readings from the collimators 150, as discussedfurther below.

The software is stored in a machine-readable media and shall beconstrued broadly to mean any type of instructions, whether referred toas software, firmware, middleware, microcode, hardware descriptionlanguage, or otherwise. Instructions may include code (e.g., in sourcecode format, binary code format, executable code format, or any othersuitable format of code).

The collimators 150 are optical instrument including a well correctedobjective lens with an illuminated calibration target at its focalplane. The emerging beam is a parallel, or collimated, beam, so that theimage of the calibration target is projected at infinity. In anembodiment, there are five collimators 150 positioned above the lens 120and the camera body 110 and are configured to output a calibrationtarget projection. The collimators 150 are positioned such that theoutput calibration target projection converges on the infrared sensorwithin the camera body 110, through the lens 120. The angled arrangementof the collimators is designed to define the whole area of image sensoraccording to the camera's apparent field of view (FOV). In anembodiment, a shutter mechanism (not shown) is placed between the lens120 and the collimators 150, such that the shutter can be opened andclosed as the position of the lens 120 is adjusted, to provide anefficient manner of calibrating the lens between various positions.

Each collimator 150 includes three main parts: a black body, a target,and a collimating lens system. The parts of the collimator 150 aredisposed within a structure of the collimator and are not shown inFIG. 1. In an embodiment, the black body is an electrically controlleddevice that is used as a highly stable background radiation source forthe target. In an embodiment, it provides a difference of 10 degreesrelative to a room ambient temperature. The camera sensor is positionedtoward the black body, such that when the lens 120 is in place, theimage produced by the sensor contains calibration target with abackground of the black body. When in a properly calibrated position,the projection of the calibration targets converge on the infraredsensor of the camera 110 such that when the lens 120 is in place, theMTF values are optimized for all of the calibration targets. The system100 may include multiple black bodies positioned within the FOV of thesensor used as calibration targets for the lens. The calibration targetsare further discussed below.

In an embodiment, one or more ultraviolet (UV) light sources 170 areplaces around the lens 120 and the camera body 110. An adhesive can beused to secure the lens 120 to the camera body 110, where the adhesiveis only cured when exposed to UV light. Thus, the position of the lens120 can be freely adjusted until an ideal position is determined, asdiscusses herein below, at which point the UV light sources 170 are usedto cure the adhesive and fix the lens in place. In a further embodiment,alternative curing mechanism are used instead of a UV curing mechanism,such as visible light curing, temperature-based curing, chemical curing,and so on.

FIG. 2A is a schematic diagram of a calibration target 200 according toan embodiment. The target may include a black body designed to provide atemperature difference as a reference of thermal radiation, and reveal aportion of the black body arranged in a certain pattern that can berecorded by the detector and analyzed by the image processing software.In an embodiment, an example pattern includes the calibration target 200with a circular shape and a portion of the circular shape exposed toreveal a black body. For example, a wedge 210 having a specific angle,e.g., an angle of 104 degrees (90 degrees of a quarter circle, with anadditional 7 degrees 220 extending outward from each axis of the wedge)is shown. In an embodiment, the size of the wedges 210, e.g., the angleof the wedge, is adjustable, which allows for the control of the patternappearance, and supports a variety of different patterns to supportvarious application needs. The straight edges, set angle, and curvedouter perimeter of the wedge shape provides different useful referencepoints to assist in determining sharp focus and calibration of the lens.Having 5 calibration targets 200 placed at defined parts of the FOV ofthe lens allows for greater optimization of the lens position.

FIG. 2B is an example screenshot of multiple calibration targets 200 assee through a calibration system. The calibration targets 200 arepositioned to maximize coverage of an FOV of the image sensor. In anembodiment, five calibration targets 200 are used, where one target isplaced toward each corner and one target is placed in the center of theframe. The calibration targets 200 are visible through a collimator,e.g., the collimator 150 of FIG. 1. Namely, the five collimators mayeach contain one calibration target 200 and are positioned to fill theFOV of the image sensor.

FIG. 3 is an example screenshot of multiple modulation transfer function(MTF) charts 300 projected onto an image of the calibration targets. AnMTF is a tool used to measure the imaging quality, including thecontrast and the resolution of an optical device. The MTF graph displaysthe contrast as a function of spatial frequency. In an embodiment, themiddle of the image sensor detects higher MTFs compared to theextremities of the sensor. In the disclosed embodiment, each section ofthe frame that contains a calibration target 200 is provided with an MTFchart 300. The positioning of the lens is adjusted, e.g., by controllingthe hexapod 145 and robotic 140 holding the lens 120 of FIG. 1, untileach of the MTF charts 300 is optimized. In an embodiment, software isused to analyze the local MTF responses in test images from the targetto provide feedback for controlling the hexapod 145 in order to adjustthe lens 120 position.

The calibration process includes a converging routine that uses the MTFchart 300 data as a metric in the determination for an optimal positionfor the lens. In an embodiment, the converging routine takes intoconsideration the measurements from five targets: one in the middle andone at each of the four corners of an image. In the shown example, theconverging routine determines at optimal position where for spatialfrequency of 50, the received MTF values is approximately 0.2 for eachof the MTF charts 300.

In an embodiment, the exact lens positioning 310, e.g., measuring inmillimeters and degrees from a point of reference, is determined andsaved for future reference.

FIG. 4 is an example flowchart 400 illustrating a method for attachingand aligning an infrared camera lens according an embodiment.

At S410, an adhesive is applied to a lens configured for an infraredcamera. The adhesive is formulated to be set and cured when exposed to acuring catalyst, such as an ultraviolet (UV) light, a temperaturechange, a chemical reaction, and so on. In an embodiment, the lens ishandled with a robotic arm, such that the adhesive is applied to thecircumference of the lens.

At S420, the lens, with the applied adhesive, is placed above the camerabody while still being held, e.g., by the robotic arm. Thus, thepositioning of the lens can still be adjusted by the robotic arm or ahexapod attached thereto, while the adhesive has not yet been cured.

At S430, the ideal lens position is determined based on calibrationtarget images and MTF charts associated with those targets, as discussedabove in FIG. 3. The position of the lens is adjusted based on feedbackfrom an MTF chart, such that the resolution and contrast of the imagefrom the camera upon which the lens is placed is maximized in all imageregions, e.g., in the four corner regions and a center region with oneregion assigned to one calibration target. In an embodiment, if all ofthe MTF charts associated with each calibration target images cannot bemaximized in a single position, the position that produced the bestresolution and contrast uniformly among all the calibration targetimages is used.

At S440, the position of the lens is adjusted based on the determinedideal position.

At S450, the adhesive is cured and the lens is fixed in place. In anembodiment, curing is accomplished by exposing the adhesive to intenseUV light from multiple directions in order to ensure uniform curing. Ina further embodiment, curing is accomplished by alternative catalysts,such as a visible light source, a temperature change, a chemicalreaction, and so on.

FIG. 5 is an example setup of an infrared lens alignment system andcuring lights, according to an embodiment. The robotic arm 140 holds thelens 120 above the camera body 110, which contains an infrared imagesensor (not shown). Multiple UV light sources 170, e.g., UV lightemitting diodes (LEDs), can be distributed around the lens 120 toprovide an even amount of light. The UV light produces a photochemicalprocess which hardens certain resins that can be used as an adhesive forthe lens 120. In an embodiment, four high-intensity spot curing LEDsoperating on a 365 nm wavelength are used. In a further embodiment,other curing techniques may be used, such as visible light curing,lasers, halogen or tungsten lights, and the like.

The various embodiments disclosed herein can be implemented as hardware,firmware, software, or any combination thereof. Moreover, the softwareis preferably implemented as an application program tangibly embodied ona program storage unit or computer readable medium consisting of parts,or of certain devices and/or a combination of devices. The applicationprogram may be uploaded to, and executed by, a machine comprising anysuitable architecture. Preferably, the machine is implemented on acomputer platform having hardware such as one or more central processingunits (“CPUs”), a memory, and input/output interfaces. The computerplatform may also include an operating system and microinstruction code.The various processes and functions described herein may be either partof the microinstruction code or part of the application program, or anycombination thereof, which may be executed by a CPU, whether or not sucha computer or processor is explicitly shown. In addition, various otherperipheral units may be connected to the computer platform such as anadditional data storage unit and a printing unit. Furthermore, anon-transitory computer readable medium is any computer readable mediumexcept for a transitory propagating signal.

As used herein, the phrase “at least one of” followed by a listing ofitems means that any of the listed items can be utilized individually,or any combination of two or more of the listed items can be utilized.For example, if a system is described as including “at least one of A,B, and C,” the system can include A alone; B alone; C alone; A and B incombination; B and C in combination; A and C in combination; or A, B,and C in combination.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the principlesof the disclosed embodiment and the concepts contributed by the inventorto furthering the art, and are to be construed as being withoutlimitation to such specifically recited examples and conditions.Moreover, all statements herein reciting principles, aspects, andembodiments of the disclosed embodiments, as well as specific examplesthereof, are intended to encompass both structural and functionalequivalents thereof. Additionally, it is intended that such equivalentsinclude both currently known equivalents as well as equivalentsdeveloped in the future, i.e., any elements developed that perform thesame function, regardless of structure.

What is claimed is:
 1. A system for optical alignment and calibration ofan infrared camera lens, comprising: a lens support mechanism configuredto adjust a position of an infrared camera lens relative to a camerabody wherein the lens support mechanism further comprises: a hexapodplatform configured to move in six degrees of freedom; and a robotic armconfigured to manipulate the position of the infrared camera lens, therobotic arm extending from the hexapod platform and being coupledthereto so as to be continually oriented parallel to an orientation ofthe hexapod platform and to maintain the infrared camera lenscontinually oriented parallel to the orientation of the hexapodplatform; at least one collimator configured to output infrared rays,wherein the at least one collimator is positioned such that the outputinfrared rays converge on an infrared sensor within the camera bodythrough the infrared camera lens; and a curing catalyst configured tocure an adhesive placed on the infrared camera lens when an ideal lensposition is determined.
 2. The system of claim 1, wherein the hexapodplatform is a Steward platform having three pairs of actuators.
 3. Thesystem of claim 1, wherein the at least one collimator includes a blackbody configured as a calibration target for the infrared camera lens. 4.The system of claim 3, wherein the lens support mechanism is configuredto adjust the position of the infrared camera lens based on a modulationtransfer function (MTF) chart associated with the calibration target. 5.The system of claim 1, wherein the curing catalyst is an ultraviolet(UV) light source.
 6. The system of claim 5, further comprising:multiple UV light sources placed evenly around the camera body.
 7. Thesystem of claim 1, wherein the curing catalyst includes at least one of:a visible light source, a temperature change, and a curing chemicalreaction.
 8. A method for optical alignment and calibration of aninfrared camera lens, comprising: applying an adhesive to an infraredcamera lens, wherein the adhesive is configured to be cured by a curingcatalyst; placing the infrared camera lens on a camera body using anadjustable arm extending from a hexapod platform and being coupledthereto so as to be continually oriented parallel to an orientation ofthe hexapod platform and to maintain the infrared camera lenscontinually oriented parallel to the orientation of the hexapodplatform; determining an ideal lens position based on at least acalibration target and a modulation transfer function (MTF) chartassociated thereto; adjusting the position of the infrared camera lensbased on the determined ideal lens position using the adjustable arm;and curing the adhesive with the curing catalyst and fixing the infraredcamera lens in place.
 10. The method of claim 8, wherein the determiningof the ideal lens position is based on optimizing resolution based onthe MTF chart.
 11. The method of claim 8, wherein determining of theideal lens position is based on optimizing contrast based on the MTFchart.
 12. The method of claim 8, wherein the curing catalyst includesat least one of: an ultraviolet light source, a visible light source, atemperature change, and a curing chemical reaction.